coder
diff --git a/‎net/dns/resolver/forwarder.go
Lines changed: 2 additions & 1 deletion b/‎net/dns/resolver/forwarder.go
Lines changed: 2 additions & 1 deletion
diff --git a/‎net/dns/resolver/neterr_darwin.go
Lines changed: 0 additions & 30 deletions b/‎net/dns/resolver/neterr_darwin.go
Lines changed: 0 additions & 30 deletions
diff --git a/‎net/dns/resolver/neterr_other.go
Lines changed: 0 additions & 16 deletions b/‎net/dns/resolver/neterr_other.go
Lines changed: 0 additions & 16 deletions
diff --git a/‎net/dns/resolver/neterr_windows.go
Lines changed: 0 additions & 43 deletions b/‎net/dns/resolver/neterr_windows.go
Lines changed: 0 additions & 43 deletions
diff --git a/‎net/neterror/neterror.go
Lines changed: 18 additions & 0 deletions b/‎net/neterror/neterror.go
Lines changed: 18 additions & 0 deletions
diff --git a/‎net/neterror/neterror_windows.go
Lines changed: 17 additions & 0 deletions b/‎net/neterror/neterror_windows.go
Lines changed: 17 additions & 0 deletions
@@ -25,6 +25,7 @@ import (
 	dns "golang.org/x/net/dns/dnsmessage"
 	"inet.af/netaddr"
 	"tailscale.com/hostinfo"
+	"tailscale.com/net/neterror"
 	"tailscale.com/net/netns"
 	"tailscale.com/net/tsdial"
 	"tailscale.com/types/dnstype"
@@ -482,7 +483,7 @@ func (f *forwarder) send(ctx context.Context, fq *forwardQuery, rr resolverAndDe
 		if err := ctx.Err(); err != nil {
 			return nil, err
 		}
-		if packetWasTruncated(err) {
+		if neterror.PacketWasTruncated(err) {
 			err = nil
 		} else {
 			metricDNSFwdUDPErrorRead.Add(1)
 
@@ -40,3 +40,21 @@ func TreatAsLostUDP(err error) bool {
 	}
 	return false
 }
+
+var packetWasTruncated func(error) bool // non-nil on Windows at least
+
+// PacketWasTruncated reports whether err indicates truncation but the RecvFrom
+// that generated err was otherwise successful. On Windows, Go's UDP RecvFrom
+// calls WSARecvFrom which returns the WSAEMSGSIZE error code when the received
+// datagram is larger than the provided buffer. When that happens, both a valid
+// size and an error are returned (as per the partial fix for golang/go#14074).
+// If the WSAEMSGSIZE error is returned, then we ignore the error to get
+// semantics similar to the POSIX operating systems. One caveat is that it
+// appears that the source address is not returned when WSAEMSGSIZE occurs, but
+// we do not currently look at the source address.
+func PacketWasTruncated(err error) bool {
+	if packetWasTruncated == nil {
+		return false
+	}
+	return packetWasTruncated(err)
+}
@@ -0,0 +1,17 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package neterror
+
+import (
+	"errors"
+
+	"golang.org/x/sys/windows"
+)
+
+func init() {
+	packetWasTruncated = func(err error) bool {
+		return errors.Is(err, windows.WSAEMSGSIZE)
+	}
+}